Degeneration or disruption of the connective tissue structures of the arterial wall can cause an artery to undergo extreme dilation, or aneurysm formation. With progression of the dilation, the tension on the vessel wall increases in direct proportion to the dilation, according to LaPlace's law which states that the tension on the wall is directly proportional to the pressure times the radius. Thus, progressive dilation leads to the eventual rupture of the artery because the tension on the vessel wall increases. Beyond a certain diameter, aneurysms are likely to rupture and cause death from internal hemorrhage, and surgical replacement of the artery with a bypass graft is mandated. Such surgical treatment requires major surgery and carries a significant mortality, especially since the patients requiring this surgery are frequently old and debilitated and do not tolerate blood loss. While the majority of aneurysms which require treatment are usually located in the abdominal aorta, a variety of aneurysms do occur in other vessels. Dissecting aortic aneurysms occur in the thoracic aorta. Pseudoaneurysms and mycotic aneurysms may occur in any location and involve any size vessel.
Ideally, the problem would best be treated in elderly acteriosclerotic aneurysms by the percutaneous introduction of a self-anchoring vascular stent which would restore the vascular lumen to normal size and isolate any additional lumen or blood space from the vessel lumen. The stent would require sufficient structural integrity to provide for a framework on which an envelope of semiporous material could be attached or be developed from cellular growth of body tissue. Such a stent would prevent the development of stenosis from cicatrization. In the case of vascular stenosis, the framework itself would dilate the vessel and maintain its internal lumen. Indeed, Maas has shown that a spiral spring can prevent development of stenosis in both experimental animals and humans. Nonetheless, the introduction of Maas' spiral springs requires a core on which the springs can be wound. This core is too large to be introduced via a narrow angiographic catheter and its introduction in itself becomes a major surgical procedure which requires exposure of a major vessel such as the femoral artery through which the core and spring must be introduced via an arteriotomy. Such a procedure would not be useful in vessels having the size of the carotid artery or renal artery, but theoretically might be useful in the treatment of aneurysms of the abdominal aorta. The methods of Dotter or Amplatz utilize a single strand helically wound wire spring which is introduced through an anigographic catheter after straightening the wire. This spiral spring is manufactured from Nitanol which resumes its former shape at the elevated temperatures of the body. These single coiled wire springs do not always follow a single longitudinal axis but veer off in one direction or another and leave the longitudinal axis. Such performance seriously limits the applicability of single strand helical wire springs as an internal vascular stent.